Approximately ten percent of the United States population suffers from some discernable symptons of arthritic disease. In the worst cases, such as osteoarthritis, the disease is characterized by deterioration of articular cartilage and loss of normal joint architecture resulting in pain and limited motion. It is estimated that about 175,000 people in this country are unable to take care of their elementary hygiene because of osteoarthritis of the hip. In some instances, rheumatoid arthritis may also produce gross destruction of the articular cartilage and render people invalid.
Rehabilitation of damaged joints therefore is of great interest. Recent advances in arthroplasty, have brought some relief from pain and improvement in gait and range of motion for those inflicted with degenerative joint diseases. In total hip arthroplasty, for example, the hip joint is replaced by a mechanical ball and socket which are implanted in the femur and pelvis, respectively.
Loosening of prothetic implants is the most prevalent problem in arthroplasty, and hip arthroplasty, in particular. For example, the Mayo Clinic has reported a 24% incidence of x-ray evidence of femoral stem loosening five to seven years post-operatively. Additionally, radiological studies have shown that as many as 87% of acetabular (hip socket) components may have a radiolucent line all the way around them at the time of ten year follow-up study. Only a small percentage of these joints are clinically loose, but the lesson to date has been that radiologic finding eventually manifest themselves as clinical symptoms. Once begun, loosening is a relentlessly progressive process. Loosening usually occurs at the bone-cement interface. The fixation at this interface is a purely mechanical one. The cement acts as a grouting agent which attempts to grip the bone by keying to irregularities on and within the cortical and cancellous surface.
A number of operative factors contribute to the weakness of the bone-cement interface. Typically, the bone surface cannot be completely cleaned of contaminants, such as blood, fat and debris. In deep cavities, such as the medullary canal of femur, there also may be inadequate filling with cement and poor mechanical keying. Bone cell death is also typical due to vascular trauma from removing the trabeculae and marrow contents followed by thermal damage from the exothermic cement polymerization reaction.
Consequently, there exists a need for improving the bond between bone and cement in arthroplasty.